With regard to patches, liners used for covering the surface of the base agent layer made of a tacky ointment or the like ordinarily have a thin film configuration made of various polymer materials. In most patches, the liner is integrated with the base agent layer as the liner is stuck to the surface of the base agent layer. When such a patch is about to be used, the liner is peeled off, generally by starting the peeling at a corner portion thereof, so as to expose the surface of the base agent layer.
Generally, the base agent layer is provided in a layer form on a flexible support, and such patches of various kinds, for example, poultices, plasters, tapes, etc., are commercialized. Therefore, it is important to facilitate the peeling of the liner off the base agent layer and therefore prevent the aforementioned patch from being deformed when the liner is peeled off.
Conventionally, in order to facilitate the peeling of the liner off the base agent layer of a patch, the use of a devised liner, for example, a liner that is provided with a linear or sawtooth tear line portion or that is divided into a plurality of pieces that can be peeled off one at a time, has been considered, and a variety of so devised liners have been proposed. The following examples of such liner constructions may be cited.
1) A liner construction wherein a central portion of a liner (peelable paper) covering the surface of a base agent layer provided on a support is provided with a wavy or sawtooth line of cuts that penetrate through the liner and align with intervals therebetween, so that the peeling of the liner can be started at the cut line portion (tear line portion) (Japanese Utility Model Publication No. HEI 5-4281).2) A liner construction wherein a central portion of a liner covering the surface of a base agent layer is provided with linearly arranged perforations that penetrate through the liner, so that the perforated portion (tear line portion) will be torn and the liner will be peeled off by pulling the liner together with the base agent layer in the right and left directions (Japanese Patent Application Laid-Open Publication No. HEI 8-112305).3) A liner construction wherein two liners cover the surface of a base agent layer and overlap each other at a central portion of the base agent layer, so that the peeling of the liners will be started at an overlap portion (a portion that is not in contact with the base agent layer) located at the central portion.
These liner constructions each have an arrangement of perforations or a line of cuts which penetrate through the liner, or have in a central portion thereof a line-shaped portion of overlap of two liners.
After a patch is produced, there is a possibility that, during storage or transportation of the patch, active ingredients and constituent ingredients of the base agent layer as well as the base agent layer itself may leak or seep out through an arrangement of perforations or a line of cuts which penetrate through the liner or a portion of overlap of two liners.
If an active ingredient or a constituent ingredient of the base agent layer leaks or seeps out or the base active layer itself leaks or seeps out, reduced effectiveness of the patch or degraded external appearance will result, and the usable life or the quality of the patch will deteriorate.
Therefore, if the base agent layer contains a volatile effective ingredient or constituent ingredient or a leachable effective ingredient or constituent ingredient that readily leaches out even through a small penetrating hole or if the base agent layer itself is leachable, no liner-penetrating hole is provided in the tear line portion of the liner. Furthermore, even if the tear line portion is provided with holes that penetrate through the liner (e.g., if the aforementioned volatility or leachability of an active ingredient or constituent ingredient is not very great, or if the leachability of the base agent layer itself is not very great), it is necessary to sufficiently consider properties of the holes that penetrate through the liner (e.g., the size of the holes, and the ratio of the entire length of the penetrating hole portions and the entire length of the tear line portion).
That is, if a liner is provided with holes that penetrate through the liner, the base agent layer contacts the outside through the penetrating holes, and therefore may suffer contamination from the external environment; therefore, it is preferable that the size and length of the penetrating holes be of minimum requirement.
However, in the conventional-art liners for patches, priority is given only to the facilitation of the peeling of the liner off the base agent layer. In a present circumstance, if the base agent layer contains a volatile effective ingredient or constituent ingredient or a leachable effective ingredient or constituent ingredient that readily leaches out even through a small penetrating hole or if the base agent layer itself is leachable, no sufficient consideration, besides the aforementioned priority, is given to prevention or restraint of the leaching of the aforementioned effective ingredient or constituent ingredient or the base agent layer, or to prevention of deterioration in the usable life and quality or degradation in the external appearance or reduction in the effectiveness of the patch during storage or transportation thereof.
Consequently, there is a demand for a liner for a patch which can easily and quickly be peeled off the base agent layer of the patch and which less tends to allow deterioration in the usable life and quality, degradation in the external appearance or reduction in the effectiveness of the patch during storage or transportation of the patch.